How to load the related entities using Entity Framework and the Repository Pattern

问题

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1. I have decided to change the Generic Repository pattern and used a specific repository for each entity. However I just cant find how to make it work because in my html I need to show some fields from related entities.

2. Is it better to replace Ienumerable with Iqueryable?

Repository Interface

 public interface IApplicantPositionRepository : IDisposable
    {
        IEnumerable<ApplicationPositionHistory> GetApplicationPositionHistories(int applicantId, int positionId);
                   void Save();
    }

Repository Interface Implementation.

public IEnumerable<ApplicationPositionHistory> GetApplicationPositionHistories(int applicantId, int positionId)
        {
            return context.ApplicationsPositionHistory.Where(d => d.applicantPosition.ApplicantID == applicantId && d.applicantPosition.PositionID == positionId);
        }

Controller Method

public ViewResult History(int applicantId, int positionId)
        {
            var history=applicantPositionRepository.GetApplicationPositionHistories(applicantId, positionId);
            return View(history);
        }

Html.

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.applicantPosition.Applicant.name)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.applicantPosition.Position.name)
        </td>

回答1:

Personally I like IList<T> but thats a personal choice of course

To include a related table simply do (this syntax of not using a string for RelatedEntityName like .Include("RelatedEntityName") I think was added in 4.1 if I recall correctly:

 return context.ApplicationsPositionHistory.Where(d => d.applicantPosition.ApplicantID == applicantId && d.applicantPosition.PositionID == positionId).Include(o=>o.RelatedEntityName);

Never return IQueryable from a repository. It's not easily testable since this is very provider specific.

I would also create separate methods if the caller does not require additional details either.

回答2:

To answer your second question:

It is definitely preferable to use IQueryable instead of IEnumerable. Doing that you can do things like this:

Controller:
public ActionResult Index(int page = 1, int pageSize = 10)
{
    IQueryable<Entity> items = repository.GetEntities();

    items = items.ApplyPaging(page, pageSize);

    return View(items);
}

You could create an extension method off of IQueryable called ApplyPaging that looks like:

public static class QueryableExtensions
{
    public static IQueryable<T> ApplyPaging<T>(this IQueryable<T> source, int page = 1, int pageSize = 10)
    {
        return source.Skip((page - 1) * pageSize).Take(pageSize);
    }
}

If it was IEnumerable then the paging could be done by the client instead of the database building the query correctly.

来源：https://stackoverflow.com/questions/7917261/how-to-load-the-related-entities-using-entity-framework-and-the-repository-patte